Skipjack Tuna

It is a streamlined, fast-swimming pelagic fish common in tropical waters throughout the world, where it inhabits surface waters in large shoals (up to 50,000 fish, often in combination with other scombridaes), feeding on fish, crustaceans, cephalopods, and mollusks. It is an important prey species for sharks and large pelagic fishes and is often used as live bait when fishing for marlin. It has no scales, except on the lateral line, and circling around the body behind the head forming a large, thick band called a "corselet". Like other tuna, it lacks a swim bladder, and must keep swimming to stay buoyant. It commonly reaches fork lengths up to 80 cm (2 ft 7 in) and a mass of 8–10 kg (18–22 lb). Its maximum fork length is 108 cm (3 ft 7 in), and its maximum mass is 34.5 kg (76 lb).

Skipjack tuna or katsuo (鰹/かつお) is used extensively in Japanese cuisine. It is eaten raw in sushi and sashimi, as well as slightly seared in katsuo tataki. It is also smoked and dried to make katsuobushi, and the shavings are commonly used to make dashi (soup stock). Katsuobushi flakes are also used as seasoning, such as in onigiri (rice balls) or on top of tofu. The raw viscera of skipjack tuna is salted and fermented to make shutō, a type of shiokara.

The fish's fat content changes during migrations along the Japanese islands. When they migrate north in summer, they are called hatsugatsuo ("first katsuo") or noborigatsuo ("ascending katsuo"), and have a lesser amount of fat. When they migrate south in autumn, they are called modorigatsuo ("returning katsuo") or kudarigatsuo ("descending katsuo"), and have a high level of fat.

Skipjack tuna are batch spawners. Spawning occurs year-round in equatorial waters, but it gets more seasonal further away from the equator. Fork length at first spawning is about 45 cm (18 in). It is also known for its potent smell.

It is an important commercial and game fish, usually caught using purse seine nets, and is sold fresh, frozen, canned, dried, salted, and smoked. In 2018, landings of 3.2 million tonnes (3.5 million short tons) were reported, the third highest of any marine capture fishery (after Peruvian anchoveta and Alaska pollock).

Countries recording large amounts of skipjack catches include the Maldives, France, Spain, Malaysia, Sri Lanka, and Indonesia.

Skipjack is the most fecund of the main commercial tunas, and its population is considered sustainable against its current consumption. Its fishing is still controversial due to the methodology, with rod and reel or fishery options being promoted as ecologically preferable.